Energy intake is the most difficult part of the energy balance equation to measure. Using an in patient computerized vending machine system, food intake has been measured over 180 individuals. In individuals undergoing the study more than once the intra-class correlation coefficient is very high (r=0.9) indicating that these studies although performed in an inpatient setting are very reproducible. Predictors of food intake in the past have demonstrated that individuals with lower fasting ghrelin concentrations (a hormone which is associated with increased food intake) actually ate more. Higher respiratory quotient, the ratio of carbohydrate oxidation to lipid oxidation, is known to predict weight gain. The mechanism of this increase in weight was thought to be secondary to a lower lipid oxidation in these individuals. Higher respiratory quotient measured during weight maintenance also predicted food intake during the ad-libitum vending machine study. However the component of respiratory quotient which best predicted food intake was higher carbohydrate oxidation indicating a role for carbohydrate (likely glycogen) balance in the regulation of short term food intake. In our vending machine study, night time eating was common, occurring in 30% of individuals. Night Eating Syndrome has been identified as a possible eating disorder leading to obesity. Although not specifically characterized as having night eating syndrome, individuals who eat at night, eat predominantly carbohydrate, and tend to gain weight at follow-up.